Glial brain tumors are induced with 100% yield in neonatal rats after intracerebral inoculation with .002 ml of high titer Avian Sarcoma Virus. Capillary endothelial cell defects in these tumors permit the passage of substances normally excluded in normal brain. Current studies include determination of the frequency, distribution, and permeability characteristics of these endothelial defects using tracer compounds of varying molecular size, some of which will be radioactively labeled with tritium. Correlative studies will be done with transmitted and differential interference light optics and electron microscopy, autoradiography, and quantitative scintillation counting. A model will be developed for the study of tumor cell kinetics of this autochthonous glioma using H3-Thymidine autoradiography. Tritium labeled cancer chemotherapeutic drugs will be studied in the same tumor system to determine their accessibility, concentration, and location within the tumor. Plans also include initiation of a project to induce neuroectodermal tumors of the retina, using the same virus.